This invention relates to a process and apparatus for molding outer and inner soles and a sole welt of thermoplastic material on to shoe uppers.
Generally soles of thermoPlastic material molded to shoe uppers have a non-abrasive outer sole and an inner sole of foamed material having high elasticity yet low abrasion resistance and interposed between the outer sole and the shoe upper.
The molding operation can be carried out using a circular turntable installation having a plurality of molding stations.
Generally the molding apparatus comprises a pair of lateral side mold parts, a bottom punch, a counter punch and a last supported shoe upper to facilitate the molding of first the inner sole and then the outer sole.
To form the outer sole, the side parts, the bottom punch and the counter punch define a mold cavity with a volume corresponding to the volume of the outer sole to be formed. The two side parts of the molding apparatus define in their closed position a feed channel by means of which the plasticized thermoplastic material is injected to form the outer sole. Then the counter punch is removed and the last supported shoe upper is slid on the side parts for forming a mold cavity for the inner sole. When removing the counter punch an infeed gate is released through which the foamed plasticized material is injected to form the inner sole.
Otherwise the inner sole may be injection molded first followed by injection molding of the outer sole such that the material for the inner sole is first injected into an intermediate space formed by the side parts, the bottom punch and the shoe last which is slid with the shoe upper mounted on the side parts, by means of an infeed gate also defined by the two side parts of the mold. After the inner sole is formed, the bottom punch is lowered, forming another mold cavity and the material for the outer sole is injected through another infeed gate, released by the bottom punch.
West German patent No. 36 00 682 discloses molding apparatus having at least one last supported shoe upper and a pivotable mold carrier supporting two pairs of opposed bottom mold parts, and a confronting mold plate formed as a counter punch and a pair of transversely movable side molds for forming molded soles such as outer soles of an elastomer and an inner sole of a mixture of isocyanate and a polyol which completely reacts into polyurethane. A pivotable last rotary head has a pair of oppositely extending lasts for supporting the shoe uppers.
The bottom mold part of the pivotable mold carrier interacts in successive work cycles with an injection mold for forming an outer sole. One of the bottom mold parts containing a formed outer sole forms together with the laterally movable side mold elements a mold cavity for forming the inner sole. The apparatus is especially utilized for molding shoe soles with an elastomeric outer sole and a foamed polyurethane inner sole.
Known leather shoes with an inner sole and a leather outer sole generally have a peripheral continuous edge laterally extending above the base of the shoe upper, and has a peripheral, continuous sole welt cemented or sewn in place.
For leather shoes this self-contained sole welt has an aesthetic function and for sport shoes, it has, for example, a double seam.
In shoes having pointed soles of thermoplastic material the shoe upper has a tendency to shear relative to the outer sole as caused by the low lateral stability of the foamed inner sole which is of a very soft material for cushioning.
For molded soles this lateral stability can be significantly improved if the shoe uppers have continuous sole welts, i.e., welts closed upon themselves.